The present invention relates generally to a rolling mill, and more particularly to a rolling mill to roll materials into products such as steel bars, wires, and pipes. The word of "products" used in this specification means a concept including steel bars, wires, and pipes.
A number of four-roll or three-roll rolling mills arranged in series roll material in four or three directions repeatedly, reducing its sectional area gradually, to form it into a desired shape of desired dimensions.
FIGS. 10 and 11 show a typical four-roll rolling mill used for such rolling work as mentioned above.
The rolling mill has an input shaft 101, which drives the four rolls 102, 103, 104, and 105. Each of the four rolls 102, 103, 104, and 105 has bevel gears (102b, 103b, 104b, or 105b as the case may be) on both its sides. The driving power of the input shaft 101 is transmitted through the bevel gears 102b, 103b, 104b, and 105b.
Given this structure, the size of the bevel gears 102b-105b has to be smaller than the diameter of the rolls 102-105 and, hence, the torque-transmitting capacity of the bevel gears 102b-105b is limited. Therefore, this structure can not be adopted for rolling mills of large capacity.
In FIG. 11, a four-roll rolling mill having the same structure as the above rolling mill is turned around the pass line by 45.degree. so as to protrude the input shaft to the upper right. This configuration makes a reducer to be connected to the input shaft 101 bulky and high, increasing the equipment cost and the necessary installation space.
On the other hand, the four-roll rolling mill disclosed in the Japanese Unexamined Patent Publication No. 71704/H4 has a bevel gear mounted on each of the four roll shafts and gears which are disposed on the back or the front of the housing and engages the four bevel gears to transmit the driving power.
This structure makes rolling mills thick and, hence, unsuitable to rolling mills such as stretch reducers which require to minimize the stand-to-stand spacing.
The three-roll rolling mill disclosed in the Japanese Unexamined Patent Publication No. 70305/H2 has in its housing a large-diameter hypoid gear of which the outer diameter is slightly smaller than the inner diameter of the housing. The input shaft of the rolling mill has an input hypoid gear which engages and rotates the large-diameter hypoid gear, which in turn engages the driven hypoid gears of the three roll shafts to drive the three rolls.
In this configuration, although the offsets between the center of the large-diameter hypoid gear and the driving and driven small-diameter hypoid gears are determined by the tooth profile, such arrangement as two large-diameter hypoid gears catch small-diameter hypoid gears between them is impossible, because such two large-diameter hypoid gears require offsets in two directions opposite to each other. Accordingly, only one large-diameter hypoid gear can be used in this configuration, which makes the configuration unsuitable to large-capacity rolling mills.
In accordance with the above, an object of the present invention is to provide a rolling mill which is thin and compact and has large capacity and of which the driving reducer is compact and low.
In case of a tandem rolling mill consisting of mill housings of more than 20 stands such as a stretch reducer, because housings have to be provided in accordance with its product sizes, the total number of housings comes to over 100.
Therefore, if every housing contains a driving gear mechanism, the cost of the whole equipment becomes huge.
In accordance with the above, another object of the present invention is to make compact the housings of a tandem rolling mill consisting of many rolling stands and reduce the cost of the housings.